Il-6/Stat3-Dependent Immunosuppressive Function Of Tumor-Infiltrating Dendritic Cells In Colorectal Cancer

Introduction Immunosuppression in tumor microenvironments is one of the critical issues for cancer immunotherapy. To develop more effective treatment, it is essential to overcome the dysfunction of immunity in cancer patients. Recently, it has been demonstrated that myeloid derived suppressor cells (MDSCs) have crucial roles for such immunosuppression. In the current reports, it was indicated that activation of STAT3 was required for immunosuppressive function of human MDSCs. In this study, we focused on IL-6/STAT3-signaling pathway in human monocyte-derived dendritic cells (DCs), and investigated the effects of IL-6 on antigen-presenting ability of DCs. Materials and Methods Tumor-infiltrating myeloid cells and PBMCs were collected from specimen of patients with colorectal cancers. Surface molecules , such as HLA-DR, of the cells were investigated by flowcytometry. Then, the surface molecules of monocyte-derived DCs from healthy volunteers were evaluated after the stimulation with IL-6 in vitro. IL-6-treated DCs were co-cultured with autologous T cells stimulated by using anti-CD3 antibody and cytokine production levels were investigated by ELISA. MAGE-A4-specific CD4+ T cells were generated from PBMCs ofhealthy healthy volunteers in vitro and co-cultured with IL-6-pretreated DCs in the presence of MAGE-A4 antigen. Cytokine production by antigen specific T cells were measured by ELISA. Results In this study, we found that expression levels of HLA-DR and CD86 are down regulated in tumor infiltrating CD11c+CD14+ DCs compared with peripheral monocytes. In addition, we confirmed that HLA-DR and CD86 expressions were significantly reduced by IL-6 treatment of CD11c+CD14+ DCs in vitro. The reduction of HLA-DR and CD86 expression levels were remarkably blocked in the presence of STAT3 inhibitor. IFN-γ production by T cells after TCR-stimulation was suppressed in the presence of IL-6-treated DCs compared with control DCs. Moreover, activation of MAGE-A4 antigen-specific CD4+ T cells were remarkably reduced by IL-6-treatment of DCs. Discussion Previously, it was reported that CD14+HLA-DRlow/- cells increased in peripheral blood of cancer patients and that these cells were an important population for immunosuppression. In this study, we demonstrated that IL-6/STAT3-signaling cascade was one of the regulating factors for surface expression levels of HLA-DR on DCs. In addition, we confirmed that IL-6-treatment significantly suppressed the antigen presentation by DCs for cancer antigen-specific CD4+ T cells. Generally, MDSCs were known to induce several immunosuppressive and tumor promoting factors such as VEGF, ARG1, and COX2. We are now investigating target molecules of IL-6 for dysfunction of DCs in tumor microenvironments. Conclusion IL-6/STAT3 signaling pathway regulates immunosuppressive function of human DCs, which would be a promising target for improving the effects of cancer immunotherapy. Citation Format: Yosuke Ono, Jyunya Ohtake, Shun Kaneumi, Kazutaka Masuko, Kentaro Sumida, Takuto Kishikawa, Satoshi Terada, Toshiyuki Kita, Norihiko Takahashi, Akinobu Taketomi, Hidemitsu Kitamura. IL-6/STAT3-dependent immunosuppressive function of tumor-infiltrating dendritic cells in colorectal cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3615. doi:10.1158/1538-7445.AM2014-3615